There is an increasing demand for the amino acid, glutamic acid in the form of its sodium salt; monosodium glutamate (MSG). This demand is due to the use of MSG as a flavour enhancer in food applications in amongst others meat, sauces and soya-based products.
L-glutamic acid is made commercially by fermentation especially in Japan and in the USA. Microbial strains belonging to the species Micrococcus glutamicus, Brevibacterium divaricatum, Brevibacterium aminogenes, Brevibacterium flavum, Bacillus megaterium and Microbacterium salicinovorum but also species belonging to the genus Corynebacterium amongst others have been used to obtain glutamic acid by fermentation. Yields of more than 40 g/100 g sugar supplied have been reported.
British patent GB 993,699 relates to a process for producing L-glutamic acid using a novel strain of Microbacterium ammoniaphilum it is mentioned that a wheat protein hydrolysate can be used as an amino acid source that is as a growth nutrient, urea being used as the nitrogen source. Before such a hydrolysate is used the L-glutamic acid is first removed. Ordinary carbohydrates are used as the carbon source.
Other strains which are used for the production of L-glutamic acid are disclosed in the following patents GB 964,623 (Brevibacterium divaricatum sp strain), GB 788,335 Cephalosporium species) and U.S. Pat. No. 3,042,585 (Bacillus circulans).
Patents GB 981,358, GB 1,096,882, GB 1,118,827 and U.S. Pat. No. 3,212,994 disclose the use of strains which are capable of growing on less costly carbon sources including different types of molasses.
European patent application EP 578 572 discloses a process for preparing a protein hydrolysate which is rich in glutamate. The process comprises the steps of enzymatic hydrolysis of proteinaceous material followed a by a treatment with bakers yeast. After autolysis of the yeast glutaminase is liberated which converts the glutamic acid to glutamate.
A different process for obtaining glutamic acid is via the hydrolysis of glutamine/glutamic acid rich proteins. The isolated glutamine-rich protein is hydrolysed using acid- and/or enzyme-conversion under the appropriate pH and temperature conditions. The product is further treated if necessary. Finally, the glutamic acid is obtained which may be further converted to glutamate. The drawback of this later method is that the other amino acids which are released during hydrolysis require the product to be extensively purified (three times crystallised) and furthermore that the other amino acids are lost as nitrogen containing waste.
Other patents relating to protein hydrolysate preparations and to sauces containing these hydrolysates are U.S. Pat. No. 3,852,479 and WO 95/28853.
It would therefore be useful to have a process starting from protein hydrolysates wherein the amino acids which would otherwise be lost are converted to glutamic acid/glutamate and which would also give rise to less extensive purification. The present invention provides such a process.